This invention relates generally to the field of tobacco processing and more particularly to cutting whole tobacco leaves for use in cigarettes.
The tobacco that is used in cigarettes is for the most part the lamina portion of the tobacco leaf. This is the thin, flexible portion of the leaf. The stem portion of the tobacco leaf is generally unsuitable for direct use as cigarette filler for several reasons, one of which is that the tobacco stem is more like wood than leaf and will punch holes in the wrapper of the cigarette. Therefore, the stem must be separated from the lamina prior to processing the lamina for use as filler.
The most common method of separating the tobacco lamina from the stem is threshing. In the threshing process, the tobacco leaf is beaten with a bar in order to knock the lamina off the stem. The lighter lamina is separated from the resulting mixture of stem and lamina (e.g., pneumatically) and the stem passes through additional threshing stages to remove more lamina until the stem is essentially free of all lamina.
A drawback of this method of processing whole tobacco leaf is that the lamina, the most valuable portion of the tobacco leaf, is damaged by threshing. Also, a portion of the lamina may be broken down into such small particles that it is unusable or requires significant additional processing prior to use. It is desirable that as little of the tobacco lamina be lost as possible. Additionally, certain characteristics of cigarettes are improved when longer pieces of lamina, or "longs", are included in the filler of the cigarette.
Prior attempts to avoid the threshing step in tobacco processing have met with limited success. One attempt, shown in U.S. Pat. No. 3,219,042, cut the whole tobacco leaf and pneumatically separated the stem from the leaf. The stem was then further processed and added back to the lamina. However, the long strands of lamina and stem produced by cutting the whole leaf became entangled and pneumatic separation of the cut tobacco leaf could not remove all of the stem portion without additional processing.